In signal processing, a band-stop filter or band-rejection filter is a filter that passes most frequencies unaltered, but attenuates those in a specific range to very low levels. A notch filter is a band-stop filter with a narrow stopband (high Q factor). Other names for a notch filter may include “band limit filter”, “T-notch filter”, “band-elimination filter”, and “band-reject filter”.
An LC circuit is a variety of a resonant circuit or tuned circuit and includes an inductor, represented by the letter L, and a capacitor, represented by the letter C. When connected together, an electric current can alternate between them at the circuit's resonant frequency. LC circuits are often used as filters. For example, three-element filters can have a “T” topology, wherein a low-pass, high-pass, band-pass, or band-stop characteristic is possible. The components of the filter can be chosen (e.g., symmetrical or not), depending on the required frequency characteristics of the filter.
LC circuits may be used for generating signals at a particular frequency, or picking out a signal at a particular frequency from a more complex signal. LC circuits are key components in many applications such as oscillators, filters, tuners and frequency mixers. For example, a microstrip circuit uses a thin flat conductor that is parallel to a ground plane. The microstrip can be made by having, for example, a wide strip of copper on one side of a printed circuit board (PCB) or ceramic substrate while the other side is a continuous ground plane. The width of the strip, the thickness of the insulating layer (PCB or ceramic) and/or the dielectric constant of the insulating layer determine the characteristic impedance of the microstrip.
Band-stop or notch filters may use transmission lines (t-lines) orthogonal to a signal path, which cause cancelation at certain frequencies that match resonant points in the t-line connected to the signal path. One end of the t-line is open and the total length from the signal path connection to the open end of the t-line stub and back to the signal connection (twice the stub length) causes a 180 degree phase shift and causes cancellation at particular frequencies.
However, conventional filters, e.g., t-line stub filters, can occupy large portions of a semiconductor, which, for example, prevent these portions of the semiconductor from being utilized for other purposes and/or increases the overall size of the device, which increases costs. For example, conventional filters may use series/parallel LC resonance using on-chip inductor and capacitor or a traditional open transmission line. However, each of these approaches require a large amount of semiconductor space.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.